The poorest 10% of car-owning households in the UK are mired in transport poverty, according to the RAC Foundation.
These households are spending at least 27% of their disposable income on buying and running a vehicle, the foundation said.
In contrast, similar motoring costs among the wealthiest car-owning households represent only about 12% of their disposable income.
Typically, a "poor" car-owning households spends £44 a week on motoring out of a total seven-day expenditure of £167, the RAC Foundation said.
Of the £44, a total of £16 is used to buy petrol or diesel and £8.30 goes on insurance.
The foundation said it had based its figures on analysis of "preciously unreleased" data from the Office for National Statistics.
RAC Foundation director professor, Stephen Glaister, said: "These figures should shock chancellor George Osborne, with some households mired in transport poverty.
"We already knew transport was the single biggest area of household expenditure bar none. But this spending breakdown just for car-owning households is not normally available. It lays bare the truth about the extent of transport poverty in the UK."
He went on: "There is understandable concern about home owners having to spend more than 10% of their money on heating their houses.
"But to most of us transport is another essential item and our outgoings on getting about eclipse all other domestic bills.
"The Budget is likely to tinker with the rate of fuel duty. For people already drowning under the weight of motoring costs, cutting a penny or two off the price of a litre of fuel will help but is like rearranging the deck chairs on the Titanic - ultimately futile.
"To make any meaningful difference to those on the lowest incomes, the rate will need to be cut much further."
Shadow transport secretary Maria Eagle said: "Rising prices at the pump, combined with inflation-busting fare rises on buses and trains, are putting massive pressure on household budgets as the cost of transport spirals.
"Instead of ministers increasing VAT on fuel and allowing private transport operators to get away with extortionate fare rises, it's time they acted to ease the pressure on families."